Do irreducibly complex biological systems exist?

If a complex biological system exists which we can be satisfied could not have arisen through natural selection, this would be strong evidence against the theory of evolution (and religious people would likely consider this to be evidence in favour of a creator).

Are there examples of systems for which all evolutionary accounts of their development seem far-fetched or very unlikely?

Posted: May 21st 2008


I think this is a strange question to ask an atheist – it’s like asking a creationist to justify evolution.

I do know that all of the examples I’ve seen from creationists that purport to be irreproducibly complex haven’t panned out.

I also think it’s very important to be cautious in this area because the utility of a specific feature to an organism may not be apparent.

Posted: May 23rd 2008

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SmartLX www

Maybe. Nobody’s identified one yet though.

Your initial statement is correct; this is one of those cases where the exception disproves the rule. At least, it would change the rule drastically. If a true example of irreducible complexity were found in a living (or once-living) organism, natural selection as we understand it could not have produced it and the current theory of evolution would be shown up as inadequate.

And if the sun were to rise in the southwest on Friday, all current understanding of the rotation of the earth and the physics of the solar system would be highly suspect. That doesn’t mean it’s about to happen.

We can’t prove the nonexistence of irreducibly complex biological systems any more than we can prove the nonexistence of a god. It’s a classic example of a non-falsifiable hypothesis. What we can do is debunk each claimed example as it’s brought forward.

In some cases like this, it’s possible that the way in which a system is hypothetically reduced going back in time is not the way it actually went. In the famous case of the bacterial flagellum, the tiniest outboard motor in the world, a subset of its components forms a Type Three Secretory System. The little screw propeller can serve as a little syringe instead. It may be that those components in those particular creatures were never actually used for secretion before getting into the locomotion business.

This doesn’t matter because the claim of irredicible complexity is that there is no possible way it could have formed from something less complex. To disprove it for a given example, one need not find the true path of development, only a possible one. Plausible is better.

All claimed examples of irreducible complexity so far have been answered with very plausible hypotheses as to their gradual development, the most famous examples most of all. When Michael Behe brought up the immune system in court, he was presented with dozens of books and papers on its evolution which he dismissed on the spot without reading them.

There might be a good example still waiting to be found. If critics of evolution took the time to actually rule out possible reducibility before presenting their examples, they’d have far fewer examples (probably none) and more time to look for real ones.

Posted: May 21st 2008

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